This disclosure relates to integrated circuits (“ICs”). The invention may be of particular interest in connection with ICs that are designed for relatively general-purpose use, rather than for only one particular use that has been fully specified in advance of design and fabrication of the IC. Examples of such relatively general-purpose ICs are field-programmable gate arrays (“FPGAs”), programmable logic devices (“PLDs”), programmable microcontrollers, and the like. Such general-purpose devices are designed, fabricated (manufactured), and sold so that they can support the typically differing needs of various users. Each user is able to customize the IC (e.g., by programming the IC) to perform the particular functions needed by that user.
Manufacturers of such relatively general-purpose ICs typically want to be able to provide a range of such products that are targeted to different segments of the market. For example, one segment of such a market may comprise users who need ICs that can support very high speed communication of data between multiple devices (e.g., between multiple ICs) in a system. General-purpose ICs that can support such high-speed communication tend to be relatively expensive; but for users who need such high-speed capability, the cost is justified. Another class of users of relatively general-purpose ICs may not need such high-speed data communication capability. This segment of the market does not want to pay the cost of high-speed devices, and is instead looking for lower-cost devices that do not have high-speed capability.
In addition to the above two classes of users, there are some users who mostly need relatively low-speed capability, but who also need some limited high-speed capability. For example, such a user may need an IC that can handle a number of relatively low-speed serial data signals, as well as a few high-speed serial data signals. A relatively inexpensive, all-low-speed IC cannot meet this user's need; but an all-high-speed IC (although it can meet the user's need) may be more expensive than the user is willing to pay. To more economically meet the needs of this type of user (and increase the market penetration (sales volume) of a basically low-cost IC design), it would be advantageous to economically and efficiently include some higher-speed data communication capabilities in relatively low-cost ICs that are otherwise primarily designed to support relatively low-speed data communication.